1. Field
Embodiments described herein relate to a nonvolatile semiconductor memory device.
2. Description of the Related Art
In a NAND flash memory, data is written in a page basis. One page is defined as memory cells sharing one word line. After the data program operation, a verify read (program verify) operation is performed to determine whether the data is accurately written to the memory cell. As a result of the program verify operation, when it is determined that the data is not written to the memory cell accurately, a program pulse voltage increases in stages (is stepped up) and then the same program operation and program verify operation are repeatedly performed.
When the program pulse voltage is stepped up and then the program operation is performed on one selected memory cell, an intermediate voltage applied to the non-selected memory cells may also be stepped up. In this case, there is a concern that an excessively large number of charges would be injected into the selected memory cell by the influence of the intermediate voltage. When an excessively large number of charges are injected into the selected memory cell, dispersion of the threshold voltage is more than a certain value, which makes it difficult to accurately write data to the NAND flash memory. Therefore, it is preferable to minimize the influence on the selected memory cell by the intermediate voltage applied to the non-selected memory cell.